Finely chop the onions. Heat a large pan over medium heat. Add 1 tablespoon butter and let it melt. Add the finely chopped onion and let it brown lightly (about 8 minutes). Constantly stir so it doesn’t burn. When the onion is light brown, remove from heat and let it cool down.In a large mixing bowl, add the ground chuck and 1 tablespoon sake (Japanese rice wine) and mash the beef until smooth.Now add the cooled onion, milk, egg, and panko bread crumbs. Lightly season with salt and pepper and mix well.Divide the mixture into 2 large oval patties and remove the air in each by tossing from one hand to another. It should make a slapping sound. This process will help the hamburg steak from breaking into pieces while cooking.Now lightly flatten the patties. They will fatten back up while cooking.Heat a large sauté pan on high and add oil. Brown one side of the patty and flip. Then add 2 tablespoon water and cover. Reduce to med-low heat and cook for 8 minutes.While the patties are cooking, make the sauce by combining water, sugar, mirin, soy sauce, and granulated dashi in a pot. Bring to a boil and let it boil for about 15 to 30 seconds then turn off the heat. The sauce should be light and watery (not thick). When the patties are done cooking, flip once more. Now, add a little bit of butter over the tops of each patty.Top with grated daikon and lightly pour the sauce with a spoon (about 2 to 3 spoonfuls). Serve with potatoes and other vegetables or shredded cabbage and rice.